In order to be an acceptable modeling stock, a material must have such properties that its dimensions are essentially unchanged over a wide variation in environmental conditions (temperature, humidity) so that the dimensions of a workpiece made from such stock can meet the increasingly rigid specifications imposed by end-use considerations such as those of the aerospace industry.
Laminated wood modeling stock and plaster models would presumably have some advantage of cost and ease of working, but wood models made from such stock can swell and warp when exposed to adverse weather conditions, especially high temperature and humidity causing the parts and tools made from such wood models to be out of tolerance. Plaster models are fragile.
Metals, particularly aluminum, clearly overcome the problems associated with laminated wood modeling stock, but metal is relatively expensive, heavy and difficult as well as slow to machine to the desired shape. Nonetheless, a metal such as aluminum remains the standard modeling stock for preparing large workpieces of exact dimensions.
Attempts to overcome the problems associated with aluminum, have focused on hand lay-up epoxy laminate structures. These clearly have the disadvantages of being very costly and labor intensive in their construction requirements and not being adaptable to robotic construction coupled with the built-in inescapable flaws where adjoining edges of cloth in said laminates occur. These disadvantages would be exacerbated in the preparation of very large workpieces.
The instant invention leads to cured epoxy resin modeling stock which can be easily machined to exact dimensions with numerically controlled (computer aided) cutting equipment, or by standard hand techniques, can be used at high operating temperatures (over 300.degree. F., 149.degree. C.), and whose coefficient of linear thermal expansion closely approaches that of aluminum.
U.S. Pat. No. 3,886,846 describes a method of testing the accuracy of a cutting machine tool control program. This patent relates to the now common practice of preparing a "control program" by punched card, magnetic tape, computer disc or whatever, on a machine tool to make a prototype workpiece. The control program thus prepared is then available to control the preparation of such workpieces on any similar machine tool. The invention of U.S. Pat. No. 3,886,846 provides an inexpensive, easily machined, thermosetting plastic block as a working stock to test whether the control program applied to the machine tool to be used to manufacture the actual workpieces will in practice machine the working stock to the desired dimensions. This allows for great savings in time and expense in testing the control program. The thermosetting platic block is cast polyurethane foam or extended polyester which may be glued together with standard epoxy putty.